This pilot research application responds to topic 18, Animal Models of Aging, as described in PA-00-053 that was released on 2-2-2000. The application fulfills purpose 2 of PA-00-053, which is to encourage an established investigator to enter newly targeted, high-priority areas in aging research. Our overall objective is to establish mouse models of human apolipoprotein (apo) E expression in pyramidal neurons of the brain that will correspond to naturally regulated sites of neuronal apoE production in the aging human brain. The basis for this project is our recent identification of specific enhancers in the human apoE gene cluster that direct apoE expression in pyramidal neurons of the cerebral cortex, in the CA1 region of the hippocampus, and in a neural center of the medulla. These sites in the cerebrum and the hippocampus are particularly sensitive to neurodegeneration in response to stroke and Alzheimer's disease. Our data confirm neuronal expression of the human apoE gene in specific regions of the brain. In contrast, the endogenous mouse apoE gene is not expressed in neurons. In Specific Aim 1 we will use the pyramidal neuron-specific enhancers to generate transgenic mice that express the human apoE3 isoform or the human apoE4 isoform in specific regions of the brain. We will generate additional transgenic mice with similar constructs to which a green fluorescent protein reporter sequence replaces a portion of the apoE gene. The transgenic mice will be mated with apoE-null mice to select animals that lack endogenous mouse apoE and express a single human apoE isoform under the control of natural apoE regulatory elements together with the similarly regulated reporter sequence. In Specific Aim 2, we will determine how the apoE gene in pyramidal neurons responds to neurodegenerative signals resulting from low doses of systemically administered kainic acid. We will evaluate how neuronal production of either apoE3 or apoE4 modulates pyramidal cell homeostasis in early neurodegeneration without the interference of apoE derived from astrocytes or microglia/macrophages. Visualization of the reporter gene will permit an in situ evaluation of the effect of the apoE isoforms on pyramidal neuron responses. These models will permit a direct evaluation of how the neuronal production of either apoE3 or apoE4 modulates pyramidal cell homeostasis in the major neurodegenerative disorders of aging.